# The Naked Scientists Forum

### Author Topic: nano meters  (Read 5191 times)

#### DERRINALPHIL

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##### nano meters
« on: 08/08/2007 22:15:41 »
Why do we measure things in nanometers? If I am not mistaken they are 10 to the minus 9 meters. Surely rounding it off to another 10 would be more logical?

#### another_someone

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##### nano meters
« Reply #1 on: 08/08/2007 22:41:41 »
10-10meters are in fact ångströms.

Ångströms are a measure that used to be very commonly used, but are now superseded. Nanometres are the preferred unit of that scale (the next level down are picometres, which are 10-12 metres).

Nanometres and picometres are part of the SI unit of measurement, which gives names for each additional power of 3.

http://en.wikipedia.org/wiki/SI#Units
Quote
The international system of units consists of a set of units together with a set of prefixes. The units of SI can be divided into two subsets. There are the seven base units. Each of these base units are nominally dimensionally independent. From these seven base units several other units are derived. In addition to the SI units there are also a set of non-SI units accepted for use with SI.
 SI base units Name Symbol Quantity metre m length kilogram kg mass second s time ampere A electric current kelvin K thermodynamic temperature mole mol amount of substance candela cd luminous intensity

A prefix may be added to units to produce a multiple of the original unit. All multiples are integer powers of ten. For example, kilo- denotes a multiple of a thousand and milli- denotes a multiple of a thousandth hence there are one thousand millimetres to the metre and one thousand metres to the kilometre. The prefixes are never combined: a millionth of a kilogram is a milligram not a microkilogram.
 SI Prefixes Name yotta- zetta- exa- peta- tera- giga- mega- kilo- hecto- deca- Symbol Y Z E P T G M k h da Factor 1024 1021 1018 1015 1012 109 106 103 102 101 Name deci- centi- milli- micro- nano- pico- femto- atto- zepto- yocto- Symbol d c m µ n p f a z y Factor 10-1 10-2 10-3 10-6 10-9 10-12 10-15 10-18 10-21 10-24
« Last Edit: 08/08/2007 22:44:26 by another_someone »

#### DERRINALPHIL

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##### nano meters
« Reply #2 on: 09/08/2007 11:42:48 »
This does not answer my question of why nanometer are the preferred measurement? I actually knew the infomation posted by another.

#### eric l

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##### nano meters
« Reply #3 on: 09/08/2007 12:02:57 »
Technicians and engineers simply prefer powers of 1000 (kilo - mega - giga or on the other side mili - micro - nano - pico).
There are exceptions of course :  tailors will use centimeters (in fact, centimeters are preferred to millimeters when it comes to measure the length of a person), and winemakers and brewers will count in hectoliters (probably because the tax people also do).

#### another_someone

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##### nano meters
« Reply #4 on: 09/08/2007 12:45:50 »
This does not answer my question of why nanometer are the preferred measurement?

In a sense, why not nanometres?

You say that you consider ångströms to be more logical, but ångströms were never part of a system of measurement - it was simply a unit that stood on its own.

Milli and micro units have a long established usage in many fields (millimetres and micrometres have been used by Engineers for a very long time), so it seemed logical to use those as the basis of a system of measurement, even if that meant obsoleting some of the more idiosyncratic units that did not fit into the system (or any other system).

Don't forget that the system works for all units (well, almost all units - it has not superseded larger units of time, such as hours, minutes, days, etc.; but it does apply to milliseconds, microseconds, and nanoseconds).  Having a system that is easily extensible, and can be moved to any domain (time, length, mass, etc.) makes it very easy for people to learn and apply, rather than having to teach people lots of different idiosyncratic units of measure for different purposes.

By having names for each unit of 103 (i.e. 103, 106, 109) makes for a comfortable separation between the scales.  If you designed a system with a separation of 1010, then would you try and subdivide that into smaller separations (e.g. 105), or would you leave people writing lots of zeroes for values that did not fit closely to 1010, or 10-10 values)?

#### Bored chemist

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##### nano meters
« Reply #5 on: 09/08/2007 19:42:50 »
It's not just engineers and such who use powers of 10 that are multiples of 3, most English speakers do to. Thousands, millions and billions all have words for them in English in a way that 10000 (for example) doesn't.
A nanometre is a billionth of a metre; 10^-10 of a metre would be a hundred thrillionths of a metre or a tenth of a billionth of  a metre. I don't see that as a particularly logical choice.

#### eric l

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##### nano meters
« Reply #6 on: 10/08/2007 15:22:04 »
It's not just engineers and such who use powers of 10 that are multiples of 3, most English speakers do to. Thousands, millions and billions all have words for them in English in a way that 10000 (for example) doesn't.
A nanometre is a billionth of a metre; 10^-10 of a metre would be a hundred thrillionths of a metre or a tenth of a billionth of  a metre. I don't see that as a particularly logical choice.
... but for counting years we use(d) centuries rather than millennia (millenniums ?) e.g. 1985 was read nineteen (hundred) eightyfive rather than onethousand ninehundred eightyfive.

#### another_someone

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##### nano meters
« Reply #7 on: 10/08/2007 16:02:02 »
... but for counting years we use(d) centuries rather than millennia (millenniums ?) e.g. 1985 was read nineteen (hundred) eightyfive rather than onethousand ninehundred eightyfive.

Since the year two thousand (note, we do not say twenty hundred) the usage has been more ambiguous.

Also, it is a cultural and linguistic thing.  In Hungarian, I was always taught to say "ezer kilencszáz hatvan három", which transliterates as "thousand nine hundred sixty three" rather than nineteen sixty three.

If you listen to people quoting large numbers (e.g. telephone numbers), you will find that some people will say the digits in pairs, while other people will say the digits out in groups of three (sometimes people switch between the two, particularly where the length of the number is a multiple of two or three digits, but most people tend to have a preference for one or the other).

#### The Naked Scientists Forum

##### nano meters
« Reply #7 on: 10/08/2007 16:02:02 »